The present invention relates to a luminous element for an incandescent lamp, in particular a luminous element having the shape of a double helix, with two terminals arranged at one end of the double helix. It also relates to an incandescent lamp having such a luminous element, a method for producing such a luminous element, and a device for carrying out the method of production.
A luminous element is disclosed in DE 44 20 607 (which corresponds to U.S. Pat. No. 5,811,934), see FIG. 3 there and its associated description. Such a luminous element has the disadvantage, however, that it is very susceptible to the flashovers in the region of the lowermost pair of turns. Because of tolerances in the production of the luminous element, during pinching of the luminous element, that is to say its mounting in a base, deformations are produced that lead to an exacerbation of said problem.
It is an object of the present invention to provide a luminous element for an incandescent lamp that has a reduced susceptibility to flashovers, in particular in the region of the lowermost pair of turns.
This object is achieved in the case of a luminous element for an incandescent lamp by the luminous element having the shape of a double helix with two terminals arranged at one end of the double helix. The diameter of the double helix increases continuously in the direction of the two terminals of the luminous element. The mutual spacing of adjacent turns from one another in space is enlarged by the measure according to the invention. This results in a substantially lower sensitivity to position tolerances during pinching.
The embodiment according to the invention continues to offer the advantages known from the prior art: for example, the currents flowing in the respectively adjacent turns are always in opposite directions. The individual turns therefore repel one another in opposite directions because of the filament current. By comparison with a simple helix, the electric inductance for the double helix is substantially lower, that is to say the lamp is more efficient as regards its generation of useful radiation, and emits less electromagnetic interference. Furthermore, the design of a luminous element in accordance with a double helix permits the active filament length to be adjusted continuously, since the orientation of the transverse connection of the two halves of the double helix can be selected at will with reference to the terminals. This results in a far-reaching complete design freedom for the variables of diameter, height, wire thickness and power.
In the case of a particularly advantageous embodiment, it is not only the diameter of the double helix that increases continuously in the direction of the two terminals of the luminous element, but also the lead of the turns, that is to say the spacing of adjacent turns from one another. This results in a further enlargement of a three-dimensional spacing. The second measure, that is to say the increase in the lead of the turns alone, does not achieve the above named object, since the double helix has the lowest mechanical stability at the end at which the terminals are located. Consequently, if only the lead of the turns is enlarged, this results in an even lower mechanical stability. Movements inside the body of the lamp, in particular owing to the inductive processes during switching on, therefore lead to an even greater readiness to short circuit. The sensitivity to position tolerances during pinching is also not reduced in the case of sole application of the second measure, since these position tolerances chiefly occur transverse to the longitudinal axis of the luminous element.
The purpose of the continuous increase is to bring about a continuous enlargement of the three-dimensional spacing of the turns since, when only the last two turns have a larger spacing from one another, the problem is displaced onto the last turn but one. Consequently, continuous increase is to be understood, in particular, as a linear, quadratic, cubic or exponential increase.
The invention also relates to a method for producing a luminous element comprising fixing a wire forming the luminous element on the first end of a rotationally symmetrical winding spindle whose diameter increases continuously from its first end up to a winding end section; winding the wire on the winding spindle between a first end and the winding end section, the turns being arranged offset on the winding spindle; and drawing the luminous element off from the winding spindle. Furthermore, the invention also relates to a device for carrying out the method of production.
In a particularly advantageous embodiment of the method according to the invention, the wire forming the luminous element is inserted simply into a notch on the narrow end of the winding spindle before the double helix is formed by winding the wire on the spindle. In order to observe very close tolerances, it is particularly advantageous to bend the terminals into shape as early as in the state in which the double helix is wound stably onto the winding spindle. For this purpose, each free wire end is bent over on a bent-over section of the winding spindle such that after being bent over the wire ends are orientated substantially in the direction of the longitudinal axis of the winding spindle. As a result of this there is no need to append any subsequent processing step that would have the purpose of bending the terminals into shape. This leads to a minimization of the risk of undesirably bending the luminous element out of its optimum shape. Winding the wire on the winding spindle can be achieved by rotating the wire about a fixed winding spindle, or rotating the winding spindle about its longitudinal axis between non-rotating wire feeds. In order to achieve a particularly advantageous embodiment of the luminous element, this relative movement can be performed in such a way that the lead of the turns on the winding spindle increases continuously from the narrow end of the winding spindle to the winding end section.
Further advantageous embodiments of the invention can be added from the sub claims.